A　new　online　dynamic　balancing　method　is　introduced　based　on　influencing　coefficient　method　of　discal　work　machined　on　the　CNC　vertical　turning　machine.　It　considers　the　spindle　system　as　a　rotor　system,　and　calculates　and　saves　the　amplitude　and　phase　influence　coefficients　which　are　got　from　the　testing　unbalance　and　the　vibration　response　of　the　spindle　system.　When　the　work　has　been　done,　the　primitive　unbalance　by　means　of　the　detection　and　control　system　without　halting　the　machine　is　obtained,　and　then　dynamic　balancing　operation　is　executed　according　to　the　practical　situation.　Finally,　the　experiment　shows　that　this　new　method　has　the　feature　of　high　balancing　precision,　high　feasibility　and　easy　operation.